Review for Gmail Manager by Joe Siegler
Rated 4 out of 5 stars
This has been a great addon, but as of May 15, 2008, it has stopped working with all my accounts. There were some remarks by Google recently about how they changed the login procedure for Gmail; this must have affected the plugin.
Likewise it could stand an update for the Firefox 3 betas.
To create your own collections, you must have a Mozilla Add-ons account.